Federal and State legislation require control of vehicle exhaust emissions. Oxides of Nitrogen (NOx) are one of the exhaust gas emissions that must be controlled.
Formation of NOx will occur at higher combustion temperatures. In order to reduce the occurrence of the formation of NOx gasses, exhaust gas recirculation systems have been developed which effectively reduce combustion temperatures and control emissions. Exhaust gas recirculation systems work by re-circulating a portion of the exhaust gas from an engine back to the intake manifold where it can combined with incoming air. When the mixture is compressed and ignited in the cylinder the result is a lower combustion temperature and the reduction of NOx. In order to make the recirculation of exhaust gas possible, exhaust gas recirculation systems use exhaust gas recirculation (EGR) valves to open and close the conduits that recirculate the exhaust gas back to the intake manifold of the engine.
The composition of exhaust gas includes substances that can effect the operation of the EGR valve. These substances typically adhere to the EGR valve components and restrict movement of the poppet valve, valve stem and other associated valve components. Also, it is particularly important to avoid exposing the actuator component of an EGR valve to the exhaust gas. In general contamination of an EGR valve impedes the movement of the valve and may require higher actuating force to achieve a desired valve position and exhaust gas flow. The operation of the EGR valve can be controlled in order to provide valve freeing force movements when a stuck valve situation is detected.